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Long version: This unit was purchased used. Seller demoed it for me, then it sat for about a year in my garage before I got up the courage to mess with it. The machine was exactly how the previous owner had left it -- .23 wire, 75/25 gas, feed tension at 3.

It worked great for about 30 minutes (maybe 3-4 minutes of actual welding/bead time, though not continuous). After a bit of hunting around for some more scrap, I was ready to go again. At some point in there, I knocked the gun off my table and onto the ground. That maybe just coincidence, but the machine wouldn't feed wire when I started up again. (trigger causes click, but no motor action). I'm thinking I maybe damaged the tip and that jammed the feed and "tripped" some sort of protection (or burned some sort of circuit). But that's just a theory based on what I've read in a ton of 135/175 threads. Most of these are related to erratic wire speed issues versus my "no feed" situation, but hey, gotta start somewhere!

Here's what I've checked so far:

Removed all tension from wire/gun leaving a naked feed wheel. Fed wire both ways through gun to check for kinking or blocked liner.

Unplugged the unit and let it rest, thinking this would allow a thermal breaker to reset. However even without wire the trigger only generates clicks from relay (but doesn't spin motor).

Removed gun from trigger recepticle. Shorted pins there. Behavior is just like gun trigger (clicks but no motor action).

Checked power at terminals above wire feed mechanism. I set voltage at 5 and see 23 volts DC at terminals.

Checked continuity of PTC1. Closed. Jumpered (as best as I good -- this seems kinda iffy to get in there safely and effectively) and got same clicking result.

Checked legs of Q1, Q4, Q8. No continutity between legs -- I *think* that is something I'm supposed to be checking .

Q5 seems to get the most attention as problematic on the 135/175, but on this board, Q5 is a really tiny 1/2 round unit -- no heat sink like I've seen in most of the other thread.

Next step?: I guess I'll try to re-flow the solder for PTC1. I'm thinking a brittle joint could be causing it to act open. And maybe I'll order one and replace it for the heck of it.

But that's all I can come up with. The board is on my desk now. I'm happy to take measurements (I have an autoranging dmm, but no clamp for amperage -- I'll buy one though if that helps!), if anyone can point me in the right direction.

Going off what your telling me, the cr3 points are stuck . Give it a light twack, it may free itself.

Whoops missed this. Is the CR3 one of the white relays? I can identify CR1, but the other relay overlaps the label and I just see CR. I'm going to go with it being 3.

And by light tap....

like with a screwdriver handle? Tiny jewelers hammer? Just wondering how much force. Oh, and do I want to do the tapping while board is out, or is it something I tap while I'm activating the trigger circuit?

Going off what your telling me, the cr3 points are stuck . Give it a light twack, it may free itself.

Thanks.

Well, I tried whacking both relays just in case. Both in and out of the welder. I'm afraid of smacking them too much - seems like I could damage other components on the board. At any rate, it didn't change anything.

Is there a continuity test I can do on the relays to rule them out? or should I just start replacing stuff? (the relay for starters and maybe the PTC1 because I'm in there)?

Better off just replacing the board, obviously there is no power going to CR3 to run the motor, Could be a linear, really could be anything. Now ALL boards have a fuse, without looking at a simular board, its likely going to be a low ohm resistor. Just don't know where it is. I'll do some reasearch tomorrow.

Better off just replacing the board, obviously there is no power going to CR3 to run the motor...<snip> ... I'll do some research tomorrow.

Thanks. Any info you can throw my way would be helpful. I'm guessing a photo isn't detailed enough, but I can upload a high-res version somewhere.

I kinda like to avoid a board replacement (I'm guessing $200?) .... it hardly seems worth it to throw that much (more) money into an MM135, but it would be equally silly to trash a barely-used welder, too.

Does anyone know about the red-disc shaped resistor (?) RV1 -- it's glued to the potentially problematic relay CR3? Is that supposed to act like a fuse/breaker like PTC1? Should there be continuity of any sort across it? It's wide open -- no resistance at all.

I took a look at the board print for the one you have there. You have weld output so
that tells us that the CR-3 is working. If the PTC is good that leaves the CR-1 relay
and the Q-1 transistor as the most likely causes. The RV-1 is a MOV and would not be
related to the issue you have right now, it is there to handle power spikes.

I took a look at the board print for the one you have there. You have weld output so
that tells us that the CR-3 is working. If the PTC is good that leaves the CR-1 relay
and the Q-1 transistor as the most likely causes. The RV-1 is a MOV and would not be
related to the issue you have right now, it is there to handle power spikes.

Thanks Kevin. I think I've seen replacement part numbers for both of those. For the few bucks they'll cost, I figure I should at least tackle replacing those before getting a whole new board (or scrapping the entire welder)!